Generate Token.cs

 public string GenerateOTP(User user, int OTPLength)
        {
            string[] AllowedCharacters = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" };
            string OTP = String.Empty;

            string sTempChars = String.Empty;

            Random rand = new Random();

            for (int i = 0; i < OTPLength; i++)

            {

                int p = rand.Next(0, AllowedCharacters.Length);

                sTempChars = AllowedCharacters[rand.Next(0, AllowedCharacters.Length)];

                OTP += sTempChars;

            }
            if (user.EmailValidationToken == OTP)
            {
                GenerateOTP(user, OTPLength);
            }
            return OTP;
        }